The present invention relates to industrial control systems and in particular to a human/machine interface (HMI) used in an industrial control system.
Industrial controllers are special purpose computers used for controlling industrial processes or manufacturing equipment. Under the direction of a stored program, the industrial controller examines a series of inputs reflecting the status of the control process and changes outputs affecting the control of the process. The inputs and outputs are most simply binary, that is "on" or "off", however, analog inputs and outputs taking on a continuous range of values are also used. The binary inputs and outputs may be represented by single bits of data. The analog inputs and outputs may be represented by multiple bit data words.
In one common architecture for industrial controllers, a central processor executes a control program during which it reads and writes input and output values (I/O) from and to an I/O image table. The I/O image table is a local memory that collects the values of all inputs and outputs of the control system and which can be rapidly accessed without the complex communication protocols needed to exchange data directly with remote I/O modules. Thus, the I/O image table simplifies and speeds the execution of the control program.
Normally, separate circuitry, operating asynchronously to the processor, refreshes the VO image table by communicating with one or more I/O modules in a scanning process. The I/O modules are distributed about a factory to be near the machinery with which they communicate and communicate with the central processor via a high speed network as is known in the art.
The data that characterizes the control process may be displayed at a central location, for example, in a terminal connected to the central processor allowing an operator to monitor the operation of the process. At times, it may be also desirable to have such control data or portions of the control data displayed at various locations throughout the factory. Further it may be desirable to allow operators to input data to the control process from these different locations.
Accordingly it is known to incorporate into the control system a number of remote human/machine interfaces (HMI) to provide for such input and output at various locations about the factory. An HMI may be a simple display providing an indication of the status of the control process, or may be an industrially hardened computer terminal allowing for both the display of more complex types of control data and for the input by the operator of data. Such HMIs include internal programs or received data from a program running on the central processor to provide a local picture of the control process related to the machines near which they are located. Historical data representing the operation of the machine may also be displayed on the HMI.
Installing an industrial control system often requires the preparation of a customized control program and it is typical as the control process evolves that the control program will be modified. For these reasons, it is desirable that the control system include features simplifying the troubleshooting of the control programs. The HMI makes a convenient tool for such troubleshooting and accordingly numerous HMIs may be placed throughout the factory for this purpose so that the different equipment may be observed directly while its portion of the control program is modified or its associated input or output data checked. In this capacity, the HMI aids in the troubleshooting process by providing a limited view of the control data and program associated with the particular machine or group of machines located near the HMI. Thus the engineer performing the troubleshooting or monitoring process may quickly focus in on relevant information.
Ideally, an HMI might be associated with each piece of control equipment for process monitoring and troubleshooting, however this is an inefficient use of resources when the HMI is not needed on a consistent basis. Desirably the number of such devices could be minimized or eliminated while still providing the ability to monitor and troubleshoot the control system when needed.